Coping with Variability
Demand Flexibility, Micro-CHP and the Informated Grid
Dr Bob EverettOpen University EERU
The privatised UK electricity industry has concentrated on the mass production and distribution of electricity
Perhaps it should be looking more at how the energy service requirements of their customers; illumination, warm homes and refrigeration can be made more flexible to help cope with variability of supply
If variability and two-shifting is such a problem, why don’t we get rid of some of it by promoting off-peak heating? - as the French did in the 1970s and 80s….
What are the problems of the variability of wind power?
Problem 1: The wind blows for a bit and then stops..
…and then starts again
Simulated Wind Turbine O/PMilton Keynes - December 1982
0
50
100
150
0 5 10 15 20
Days
kilo
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tts
But it isn’t totally random...
In this data set there is a slight daily cyclic variation and another of approximately 5.5 days
Wind power autocorrelation functionMilton Keynes winter 82/3
-0.2
0
0.2
0.4
0.6
0.8
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0 5 10 15 20
Time lag - days
Co
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oef
fici
ent
Problem 2:
It may be possible to predict accurately the strength of approaching winds in a weather front, but not exactly when it will arrive plus or minus an hour
So we’d like:
Some long term demand flexibility of the order of several days
Lots of short term demand flexibility of around an hour
What’s on offer?
During the 1999 solar eclipse UK electricity demand fell by 2.2 GW in 20 minutes - just because lots of people found something better to do than work
Picture: National Grid
This A++ rated freezer will keep your food frozen for 64 hours after a mains interruption - alas its only rated at 115 watts
Picture: Miele
In my home I have water heating using an off-peak water heater with a 3 kW element. I don’t care exactly when it is heated up as long as I get a hot bath in the morning
My fridge is rated at 150 watts and cycles approximately once every three-quarters of an hour. I’m sure that it could be delayed by 30 minutes without any problems
The company Dynamic Demand has been promoting the use of fridges in conjunction with mains frequency sensors, essentially to carry out the standing reserve function of ‘frequency service’
This report argues that it makes no sense to sell electricity without a parallel flow of information about its use - we need a proper ‘informated grid’
If it can be put in place then new ways of buying and selling electricity will arise
Domestic metering is stuck in a bygone age
We have advanced only slightly from this mid-Victorian (gas) meter
This is my home electricity meter (installed 1997)
A spinning disk meter (invented circa 1890) with a radio controlled tariff time switch.
Even this does not actually control when my immersion heater comes on - that’s controlled by a timeclock set by me.
There have been UK studies on the problems of metering, for example net metering of domestic PV, but there is an unwillingness to pay for the necessary complex meters.
So - how will we get to an ‘informated grid’?
A new factor - Domestic Micro CHP
Philips StirlingEngine200W
generator1950
Whispergenpackaged
1.2 kW CHP2004
Experimental1kW CHP unit
1991
In the early days of small scale (circa 100 kW) CHP in the 1980s equipment reliability was transformed by ‘informating’ it.
Modem links to the suppliers allowed on-line monitoring and fault diagnosis. Servicing and rapid repairs could be carried out before problems became serious, expensive and embarrasing.
The market potential for domestic micro-CHP units is reckoned to be in the millions. This represents at least a gigawatt of generation capacity
Will this be the first domestic plant to be ‘informated’?
On-line monitoring could give increased reliability and consumer confidence and allow the design to be pushed to higher efficiencies
Picture: Whispergen
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